Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$28.68	8.568%	$31.1373	$31.14	$31.15	$31.10
Purchase #2	$135.95	5.246%	$143.0819	$143.08	$143.10	$143.10
Purchase #3	$105.35	3.609%	$109.1521	$109.15	$109.15	$109.20
Purchase #4	$160.82	11.501%	$179.3159	$179.32	$179.30	$179.30
Purchase #5	$111.78	11.362%	$124.4804	$124.48	$124.50	$124.50
Purchase #6	$133.51	8.617%	$145.0146	$145.01	$145.00	$145.00
Purchase #7	$204.77	9.190%	$223.5884	$223.59	$223.60	$223.60
7 purchase totals =	$880.86		$955.7706	$955.77	$955.80	$955.80